The present invention relates generally to telecommunications systems and methods for making and receiving calls within a satellite network, and specifically to handling incoming calls to an optimized mobile station within a satellite network.
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Services Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 12 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several base transceiver stations 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the Mobile Stations 20 currently located within the MSC/VLR area 12. If a MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that Mobile Station 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
It should be understood that the aforementioned system 10, illustrated in FIG. 1, is a terrestrially-based system. In addition to the terrestrially-based systems, there are a number of satellite systems, which work together with the terrestrially-based systems to provide cellular telecommunications to a wider network of subscribers. This is due to the fact that the high altitude of the satellite makes the satellite visible (from a radio perspective) from a wider area on the earth. The higher the satellite, the larger the area that the satellite can communicate with.
Within a satellite-based network 205, as shown in FIG. 2 of the drawings, a system of geostationary satellites 200 in orbit (one of which is shown) are used to provide communication between Mobile Stations (MS) 20 and a satellite-adapted Base Station System (SBSS) 220, which is connected to an integrated Mobile Switching Center/Visitor Location Register (MSC/VLR) 240. The MS 20 communicates via one of the satellites 200 using a radio air interface, for instance, based on the Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA). The satellite 200 in turn communicates with one or more SBSSs 220, which consist of equipment for communicating with the satellites 200 and through the satellites 200 to the MS""s 20. The antennae and satellite tracking part of the system is the Radio Frequency Terminal (RFT) subsystem 230, which also provides for the connection of the communication path to the satellite 200.
In such satellite networks 205 using geostationary satellites 200, the coverage area for a satellite 200 can be (and usually is) very large. This area can be served by a number of MSC/VLRs 240 which are connected to Public Switched Telephone Networks (PSTNs) (wireline networks), PLMNs (cellular networks) and each other. The terrestrial interconnections (trunk circuits) to these MSC/VLRs 240 are expensive to install and maintain, especially in comparison to handling the traffic over the satellite 200. Currently, the terrestrial trunk circuits are leased or owned by the operator, and in some cases, may need to be installed when the satellite network 205 is commissioned. Since the distances within the area served by the satellite(s) 200 are typically very large, the costs for these circuits can be enormous. In particular, the costs can be considerable if the circuits must cross remote areas or oceans.
Thus, as shown in FIG. 3 of the drawings, calls can be optimized using satellite resources by moving a mobile subscribers registration from a serving MSC/VLR 240a to an optimal MSC/VLR 240b. This can be accomplished by sending the Called Party Number (CPN) using, for example, an Unstructured Supplementary Services Data (USSD) string, to a Call Optimization Server (COS) 250 via the serving SBSS 220a and the serving MSC/VLR 240a. The COS 250 performs an analysis on the CPN to determine the optimal MSC/VLR 240b, e.g., the MSC/VLR 240b with either the closest connection to the called subscriber 260 or the MSC/VLR 240b with the least expensive link to the called subscriber 260. Thereafter, the address of the optimal MSC/VLR 240b is returned to the MS 20, which can then register with the indicated MSC/VLR 240b. Once the registration is complete, the MS 20 can send a SETUP message to the new MSC/VLR 240b via the new SBSS 220b, and the call can be completed.
Once the initial call has been optimized, it is handled by the optimal MSC/VLR 240b, which implies that after the initial call has been optimized, all new incoming calls will be routed to that optimal MSC/VLR 240b. However, that optimal MSC/VLR 240b may not be optimal for the new incoming calls. For example, a call that may be a local call prior to the optimization may become a long distance call if the called subscriber is moved (re-registered) to an MSC/VLR 240b that has to be reached via a long distance (most likely international) network.
It is, therefore, an object of the present invention to reduce sub-optimal routing of new incoming calls to a mobile station within a satellite network.
The present invention is directed to telecommunications systems and methods for reducing sub-optimal routing of new incoming calls to an MS that has been re-registered at an optimal MSC/VLR for an optimized call. When the MS is re-registered at the remote optimal MSC/VLR, the HLR stores an optimization indication indicating that the MS has been re-registered. Thereafter, when an incoming call to the MS is received during the time that the MS is re-registered, the HLR can forward the incoming call to a local voice mail box associated with the MS. Alternatively, the HLR can store an unavailable indication along with the optimization indication while the MS is registered at the optimal MSC/VLR. The unavailable indication instructs the HLR to send an unavailable message to the calling party. In either case, once the MS registers back with the originating MSC/VLR, the MS can be notified that an incoming call was received during the optimized call. Advantageously, either of the above alternatives will avoid setting up a long distance leg to the remote optimal MSC/VLR.
Yet another alternative is to be more selective regarding which calls are to be accepted while the subscriber is re-registered at the optimal MSC/VLR. The HLR can store a screening list containing B-numbers of calling party""s that are allowed to proceed even if higher charges are applied. Still a further alternative is to provide a special announcement to the calling party indicating that the MS has been re-registered and that higher charges may apply. The calling party may override the announcement and proceed with the call setup understanding that additional charges may apply to either calling or called party.